This invention relates to the technology of injecting a radioactive source (the xe2x80x9cseedxe2x80x9d) through an injection needle into a patient""s body for a brachytherapy. In particular, this invention relates to apparatus for controlling such a needle such that its tip will accurately reach a target position inside the patient""s body.
In the field of medicine, nuclear radiation is used for diagnostic and therapeutic treatment of pathogenic tumors. Typically, more than half of the patients inflicted with cancer require radiation therapy either as a primary or as an adjunct treatment modality. Conventional medical radiation sources used in these treatments include large fixed position machines such as linear accelerators or radioactive cobalt machines, as well as small, radioactive sources inserted locally in the tumor area. The radioisotope containing seeds are capable of producing a high dose of radiation in a pre-defined geometry of the treatment volume. This treatment is commonly referred to as brachytherapy because the radiation source is located close to or, in some cases, within the treatment volume.
The advantage of brachytherapy is that very high radiation doses can be delivered in a short time to small volumes without the delivery of excessive dose to the adjacent normal tissue. This is due to the rapid drop-off of the radiation dose rate within a few centimeter from the radioactive source. Hence, brachytherapy provides excellent results for localized control of various tumors.
In brachytherapy, a template having an array of openings for accepting a plurality of probes or needles is typically inserted in a body cavity near tumors to be treated. Probes or needles containing a radioactive seed are inserted into the openings, and their exact location is determined in reference to one or more scanned images. For anatomical regions where there is no body cavity, interstitial implantation of radioactive needles is employed.
The needles are typically long, hollow, with a small outer diameter (small gauge) and at least one sharp end to allow penetration through the tissue. Small-gauge needles tend to deflect easily when they encounter an obstruction such as calcification or a change in tissue impedance, or the phenomenon of so called xe2x80x9cneedle bowingxe2x80x9d may result if the needle continues to be pushed while its tip cannot advance accordingly.
For brachytherapy treatments, a physician prescribes a radiation dose and defines the treatment volume on scanned images of the patient""s treatment area. Images of the treatment area are obtained from modalities such as X-ray radiograph, computed tomography (CT), magnetic resonance (MR), ultrasound, or nuclear medicine scans (PET) of the patient. Based on the physician""s prescription and the scanned images, a treatment plan is devised, determining the type, activity, number, and coordinates of the radioactive seeds and the resulting radiation dose distribution. The treatment plan is optimized by maximizing the dose to the treatment volume and minimizing the dose to the adjacent normal tissues and organs. The accurate execution of the optimized treatment plan depends upon the accuracy in the radioactive seed placement and needle injection.
Needle bowing and deflection cause inaccurate placement of the radioactive seeds and result in possible underexposure of the tumor and unwanted exposure of normal tissue to harmful radiation.
In addition, bending of the needle may result in breaking of the needle in the tissue. This can cause tissue damage and may require surgery to remove the broken needle pieces.
It is therefore an object of this invention to provide apparatus with an improved control system for and methods of thrusting an injection needle with high precision for brachytherapy, capable of safely and dependably causing its tip to reach a desired target position inside a patient""s body, in spite of the possibility of the needle deflection and bowing due to conditions inside the patient""s body through which the needle is pushed forward.
It is also an object of this invention to provide a detector for detecting a bent condition of such an injection needle as it is being pushed through a patient""s body in a brachytherapy.
According to this invention, an injection device of a known kind for brachytherapy, with a hollow needle supported at one end by a main structure, is provided not only with a thruster for thrusting the needle straight in the normal longitudinal direction towards a target position but also with means for causing the needle to undergo a rotary motion and a linearly reciprocating tamping motion such that when the needle encounters an obstacle, or enters a highimpedance region, the mode of rotary and/or tamping needle motion by these means is modified such that the penetration of the needle through a patient""s body can be effected smoothly and without needle bowing or deflection.
The mode of moving the needle, including the thrusting motion, the rotary motion and the tamping motion may be modified while the user is observing a real time image of the needle as it advances through the patient""s body, in response to the warning from a deflection detector which detects a bent condition of the needle, or on the basis of earlier obtained anatomical data on the patient""s body which may be retrieved from a memory device.
With the needle motion thus controlled as the needle encounters an obstacle while advancing through the patient""s body, it can be ensured more dependably that the needle will advance straight to the target position without being deflected or bowing en route.